Recently the concept of using biological response modifiers (BRMs) has been considered for the treatment of cancer. Some BRMs are not directly cytotoxic to tumor cells, but possess qualities which change the environment of the organism. Immune stimulation and inhibition of new blood vessel growth are two biological response modification strategies with potential in the treatment of cancer. Examples of immune stimulators with known anti-tumor activity are Polysaccharide K, beta 1,3, glucan, and the Maruyama vaccine. All of which contain high-molecular weight polysaccharides and/or protein. Examples of angiogenesis inhibiting molecules include TMP-470, and angiostatin, which have demonstrated anti-tumor activity. While investigating extracts of field bindweed for anti-tumor activity, we initially tried to isolate low-molecular weight alkaloids, which are known to be toxic, and which we suspected of having traditional chemotherapeutic, or tumor-cytotoxic activity.
It was found that the low-molecular weight extracts, containing the toxic alkaloids, exhibited little anti-tumor activity, while high molecular weight extracts, which excluded the toxic alkaloids contained significant anti-tumor activity by acting as biological response modifiers.